But lately the Comic-Con surprise has felt about as fresh as your Uncle Murray’s surprise birthday party. The problem? So many of these types of moments have been orchestrated over the years that they’ve ceased to be, well, surprising. Fans now actually expect the unexpected, so if there’s even the slightest hint that something unscheduled may be coming, the eager crowd is primed for something big. Which means that if it doesn’t happen, they’re inevitably disappointed.

That disappointment was on display at the San Diego Convention Center on Thursday, as Web buzz turned into a panelist tease, which turned into … nothing at all.

At the start of the day, the flames of an online rumor about a Brad Pitt appearance for DreamWorks Animation’s “Megamind” were fanned when, early on in the panel, Pitt co-star Will Ferrell noted that a “special guest” was in the room. He then walked offstage stage to greet the special guest — and came back with … a cardboard cutout of Brad Pitt. A few fans seated near me were sure that it was all just a ploy to heighten the suspense and that the real Pitt would soon step out, but it never happened, and the crowd filed out hungry.

Later in the day, it happened again. You could practically feel the wind going out of the room when an otherwise solid panel for “The Expendables” didn’t yield co-star Arnold Schwarzenegger. Several panelists, including Sylvester Stallone, had referenced the possibility that the governor could appear, so when the moderator said the crowd was in for a “special treat,” you could understand why people were thinking that the man famous for saying “I’ll be back” would make good on his word. But the special treat turned out to be little more than the editor of the Guinness Book of World Records presenting a plaque to Stallone that honored “Rocky“ as the most lucrative sports franchise of all time. It wasn’t exactly a “Gonna Fly Now” moment.

Movie panels don’t have to one-up each other. Plenty of these gatherings can do just fine showing off some good-looking footage or involving the fans in a novel way.(Disney’s decision to have the crowd provide sound effects that will later be mixed in to “Tron: Legacy” was a nice stroke.) And doing the opposite — playing a surprise too close to the vest — can backfire too: There were zero clues during that same “Tron: Legacy” panel about the presence backstage of Guillermo del Toro. When the fanboy-beloved filmmaker stepped out at the very end and unveiled his new movie — as juicy a piece of news as you’ll find in San Diego — there was confusion from some of the attendees, who had begun to leave the room without even realizing a genre icon had taken the stage.

But the biggest mistake is teasing something that won’t happen, as Ferrell — no doubt feeling the need to address the Pitt situation — essentially did. The better move would have been to say nothing at all. Comic-Con surprises are now part of the annual script, so it’s unwise to hint at the possibility of anything that you can’t deliver. We suspect there will be a few more big reveals by the time the convention winds down on Sunday. Here’s hoping they reveal more than just some awkward planning.

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